1. Field of the Invention
The present invention relates to an automatic leveling and synchronization (ALAS) system for counterweight removal and installation used on cranes to raise and lower a counterweight evenly (counterweight remains level).
2. Description of Related Art
When a single source of supply oil (hydraulic fluid) is divided into two supplies (parallel), the majority (or all) of the total supply will go to the parallel leg that has the least resistance. The remaining supply oil (if any) will go to the other parallel leg. Hydraulic cylinders with equal areas connected in parallel will not necessarily extend or retract evenly due to unusual resistance of (and therefore flow to) each cylinder.
Conventional crane counterweight removal and installation systems use two or more identically sized cylinders in parallel hydraulic communication and connected to opposite ends of a counterweight. These conventional systems use one of two general methods for maintaining uniform or equal cylinder (and therefore counterweight) movement. The first method requires individual control of each cylinder by an operator. In this method the operator insures that the counterweight: remains level (equal cylinder movement) by individually controlling the oil flow to each cylinder. The second method requires the use of hydraulic components to maintain an exact flow of oil to each cylinder to insure that the counterweight remains level. The use of one or a combination of the following components can be used in this type of system: relief valves, flow dividers, flow dividers/combiners, orifices (resistance), and/or pressure compensated flow control valves or other hydraulic components.
First Conventional Method: Individual Control of Identically Sized Cylinders By An Operator
Use of this method requires good coordination and judgement on the part of the operator. Due to the possible and probable variances between the control devices for each cylinder, along with the probable uneven loading of each cylinder, the operator has to alter the setting of each control device and judge how level the moving counterweight really is. How level the counterweight is raised and/or lowered will thus vary from one operator to another.
While the control (and control layout) of the main functions of most cranes may be very similar, the operation and control of counterweight removal systems can differ from one crane to another. An experienced operator may be able to move from one crane to another and easily operate the main functions. That same operator, however, may not be familiar with each crane's counterweight removal system, which normally is not used frequently. This situation could result in lost time and/or the counterweight not being raised or lowered properly.
Second Method: Flow To Identically Sized Cylinders Determined By Hydraulic Components
An operator using this method of control needs only to select if the counterweight is to be raised or lowered. Hydraulic components control the supply of oil to each cylinder to maintain level counterweight movement when raising or lowering the counterweight. These components can be initially set, at a given temperature and load, to accurately deliver the proper amount of oil to each cylinder. However, slightly out of balance counterweights, differently sized (i.e., weight) counterweights, temperature changes, hydraulic valve springs taking a set (i.e., permanently deformed), component wear-in, change in oil supply (due to pump speed and/or wear), and even an oil change can effectively alter the initial settings. If the initial settings are effectively altered, the counterweight will not maintain a level position while being raised or lowered.